This post on Daring Fireball led me to this email tracker, read receipt and spy pixel blocker plugin for macOS Apple Mail. I know nothing about programming software and was able to install the plugin for my laptop using the Terminal. It’s working. If you want to check it out click on the next link.
MailTrackerBlocker is a plugin (mailbundle) for the default Mail app built-in to macOS. Email marketers and other interests often embed these trackers in HTML emails so they can track how often, when and where you open your emails. This plugin works by stripping out a good majority of these spy pixels out of the HTML before display, rendering the typical advice of disabling “load remote content in messages” unnecessary.
Browse your inbox privately with images displayed once again.